Pulse radiolysis of the aqueous ferro-ferricyanide system. I. The reactions of OH, HO₂, and O₂^- radicals

Pulse radiolysis of ferro and ferricyanide aqueous solutions is investigated at various H⁺ and salt concentrations. It has been found that association and ion pair formation may affect the reactivity toward OH, HO₂, and O₂^- radicals. The following reaction rate constants were determined (in units of M^-1 sec^-1): k((OH + Fe(CN)₆^4-)) = (1.25 ± 0.1) × 10¹⁰; k((OH + HFe(CN)₆^3-)) = (9.0 ±0.9) × 10⁹; k((OH + H₂Fe-(CN)₆^2-)) = (1.7 ± 0.5) × 10⁹; k((HO₂ + Fe(CN)₆^4-)) = (3.0 ± 1.5) × 10⁴; k((HO₂ + HFe(CN)₆^3-)) = (1.4 ± 0.1) × 10⁵; k((HO₂ + H₂Fe(CN)₆^2-)) = (1.0 ± 0.3) × 10⁴; k((HO₂ + KFe(CN)₆^3-)) = (3.0 ± 1.5) × 10⁴; k((O₂- + Fe(CN)₆^3-)) = (2.7 ± 0.9) × 10²; k((O₂^- + KFe(CN)₆^2-)) = (6.2 ±0.6) × 10³. The last two values are calculated for zero ionic strength. The formation of ion pairs has only a little effect (∼10% decrease) on the reactivity of ferrocyanide toward OH radicals.